Utah Milkweed
Asclepias labriformis M.E.Jones
A Utah endemic of the Colorado Plateau, found nowhere else on earth, and reckoned to be among the most poisonous plants on western rangeland. Creamy yellow flowers on a knee-high plant growing in dry washes where the subsoil holds water.
Also called Labriform Milkweed.
- Height
- 1 ft–1.7 ft
- Spread
- 1 ft–1.5 ft
- Flowers
- cream, yellow, green
- Bloom
- May to August
- Light
- Full sun
- Soil moisture
- Dry
- USDA zones
- 5–8
- Leaves
- Opposite, lanceolate
- Sap
- Milky latex
- Roots
- Deep taproot, resents transplanting
- Stratification
- 30 days cold-moist
- Range
- 1 state
When it flowers
Utah Milkweed blooms May to August, peaking in June and July.
How to identify it
- Erect stems to about 50 cm, hairy when young and smooth with age.
- Opposite or nearly opposite leaves, leathery, up to 15 cm long and no more than 2 cm wide, with a tuft of hair at the base of the midrib.
- Faintly scented creamy yellow to yellowish-green flowers in gently domed umbels, each flower under 1 cm across.
- Dry sandy washes and sandstone canyon country between about 3,500 and 7,000 feet, from the southern Canyonlands northeast into the Uinta Basin.
Unfamiliar words are in the glossary, and the identification key will narrow a plant down from what you can see.
Ecology and wildlife value
A monarch host within its small Utah range, and a nectar source in country where midsummer flowers are scarce. Because the whole species occupies one corner of one state, its habitat matters out of all proportion to the plant's size.
Monarchs are not the only thing that will find it. Expect large milkweed bugs on ripening pods, oleander aphids on the stems, red milkweed beetles at the flowers and, in late summer, milkweed tussock moths. Everything that lives on milkweed.
Growing utah milkweed
Not in the nursery trade and not a garden plant. It is listed here so that it can be recognized and left alone. If you find it, record it rather than collect it: the entire world population is in Utah.
Seed needs about 30 days of cold-moist stratification. Deep taproot, resents transplanting. See how to plant milkweed seed for the full method.
Cautions
Cronquist and co-authors describe this as one of the most poisonous of all western range plants, a reputation few other milkweeds carry. Treat it with real respect around livestock, and do not let it into hay. The usual milkweed advice about irritating sap applies too, but with this species the grazing risk is the serious one. More on milkweed toxicity.
Where utah milkweed grows
Recorded in 1 state: Utah.
County records from USDA PLANTS, public domain. Cross-check against BONAP and your regional flora before making management decisions.
Frequently asked questions
Is Utah milkweed really the most toxic milkweed?
It has that reputation in the range literature, where Cronquist and co-authors call it one of the most poisonous of all western range plants. Milkweed toxicity varies enormously between species, and the narrow-leaved western group is the dangerous end of it. Utah milkweed sits at that end.
Where can I see Asclepias labriformis?
Only in Utah, on the Colorado Plateau, roughly from the southern Canyonlands northeast into the Uinta Basin. It grows in dry sandy washes where the subsoil stays moist.
References and further reading
Names, ranges and conservation status here are drawn from the databases below. Where those disagree with a regional flora, trust the flora.
- Plants of the World Online 21220-2. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
- GBIF 3170345. Global Biodiversity Information Facility. Aggregated occurrence records.
- iNaturalist 126673. Community observations, photographs and phenology.
- BONAP county distribution map. Biota of North America Program. County-level range map.
- NatureServe Explorer. Conservation status ranks at global and state level.
- World Flora Online. Nomenclature and synonymy.
- Woodson, R. E. (1954). The North American species of Asclepias L.. Annals of the Missouri Botanical Garden 41(1): 1–211. The monograph the modern taxonomy of the genus still rests on. View
- Flora of North America Editorial Committee (eds.) (2026). Flora of North America North of Mexico. Oxford University Press, New York and Oxford. Accepted names, keys and descriptions for the North American flora. View
- Royal Botanic Gardens, Kew (2026). Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Nomenclature and global distribution, keyed to IPNI name identifiers. View
- Kartesz, J. T. (Biota of North America Program) (2026). North American Plant Atlas. BONAP, Chapel Hill, North Carolina. County-level distribution maps, the basis for the ranges generalized here. View
- USDA, NRCS (2026). The PLANTS Database. National Plant Data Team, Greensboro, North Carolina. State-level distribution, wetland status and nomenclature. View
- Agrawal, A. A. (2017). Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution. Princeton University Press. The standard general account of the milkweed and monarch relationship. View
Cite this page
This page is licensed CC BY 4.0. Quote it, adapt it and reuse it, including commercially, as long as you credit Milkweed USA and link back.
Milkweed USA. (2026). Utah Milkweed (Asclepias labriformis). Retrieved DATE, from https://milkweedusa.com/species/utah-milkweed/
"Utah Milkweed (Asclepias labriformis)." Milkweed USA, 2026, https://milkweedusa.com/species/utah-milkweed/. Accessed DATE.
Milkweed USA. "Utah Milkweed (Asclepias labriformis)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/utah-milkweed/.
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title = {Utah Milkweed (Asclepias labriformis)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/species/utah-milkweed/},
note = {Accessed DATE}
}